# help:crystal oscillator circuit

#### aidafiza

Joined Jun 2, 2008
17
hi..i hv a problem designing a crystal oscillator circuit..it looks like the gate circuit in figure below but without the NAND gate..the crystal have a frequency of 8Mhz..how do i get the value of the resistors?

#### Wendy

Joined Mar 24, 2008
21,919
I assume the triangles with BCE on it are transistors, correct? If they are then you are talking transistor biasing, mostly.

#### SgtWookie

Joined Jul 17, 2007
22,210
Ahhh - the gate circuit without the NAND gate?

What are you using instead to excite the crystal?

#### Wendy

Joined Mar 24, 2008
21,919
If I'm right the crystal is on the emitter. We are talking very unconventional schematic symbols here.

It would help a lot to know where the drawings came from.

#### aidafiza

Joined Jun 2, 2008
17
the gate circuit doesn't have any transistors..and in the circuit i want to use,it is similar to the circuit written "Gate" in the figure but it doesnt hv the NAND gate..how the crystal is excited im not sure since it is connected to the CLK pin of a chip..i guess the best way for me to get the value of the resistors is by doing the good old try n error..i hope i'll find a value..thanx anyways..

#### SgtWookie

Joined Jul 17, 2007
22,210
the gate circuit doesn't have any transistors..and in the circuit i want to use,it is similar to the circuit written "Gate" in the figure but it doesnt hv the NAND gate..how the crystal is excited im not sure since it is connected to the CLK pin of a chip..i guess the best way for me to get the value of the resistors is by doing the good old try n error..i hope i'll find a value..thanx anyways..
What is the chip that you are trying to clock? Do you have a link to a datasheet?

If the datasheet has no information in it about clocking it using an xtal, go to Texas Instrument's site and get their datasheet for a CD4045B CMOS IC.

On the first page there's a similar xtal oscillator, with suggested values given in the text on the left side of the page.

#### Wendy

Joined Mar 24, 2008
21,919
There are a lot of configurations for Xtal oscillators. This is a good place to ask questions about them. I'm working with a 4060 version myself.

BTW, nice detective work Sarge.

#### aidafiza

Joined Jun 2, 2008
17
the circuit is connected to a Zilog Z85C30..thanx for your tips on the CD4045B ic..it was a great help..im off to test my circuit..

#### SgtWookie

Joined Jul 17, 2007
22,210
OK, I think you'll run into trouble with that circuit. You're going to need to use an inverter or two, perhaps a NAND gate, in order to get a clock signal out of that xtal.

If you use TTL level IC's, that'll change the values for the resistors.

You might try a CMOS 4093 (Quad Schmitt-trigger NAND) or 40106 (Hex Schmitt-trigger inverters). Run the unused gates/inverters in parallel to buffer the output of the xtal clock circuit.